A VVT-controller adjusting a valve timing of an intake valve includes: a variable-camshaft-timing mechanism which adjusts a rotational phase of an intake camshaft by using of a differential hydraulic pressure between a pressure in an advance chamber and a pressure in a retard chamber; an oil flow control valve (OCV) which controls the differential hydraulic pressure; and an electric actuator which drives the OCV. The variable-camshaft-timing mechanism is referred to as a VCT-mechanism, hereinafter.
The electric actuator is driven by an engine control unit (ECU) to control an operation condition of the OCV, whereby the hydraulic pressure in the advance chamber and the retard chamber is controlled so that the rotational phase of the camshaft is adjusted relative to the crankshaft.
While the engine is ON, a vane rotor of the VVT-controller receives torque fluctuations transmitted to the camshaft. The hydraulic pressure in the advance chamber and the retard chamber also fluctuate due to the torque fluctuations transmitted to the vane rotor from the camshaft.
As a result, the hydraulic pressures in the advance chamber and the retard chamber alternately increase and decrease due to the torque fluctuations. In order to restrict deterioration in responsiveness of the VVT-controller, a check valve is provided in an oil-supply passage so as to prevent a reverse flow from the chambers to an oil pump.
JP-2005-325841A (US-2005/0252561A1) shows an arrangement of a check valve. A spool has a spool passage therein. Working fluid flows in the spool passage toward an advance chamber and a retard chamber. A check valve is arranged in this spool passage.
The check valve includes a ball valve opening/closing the spool passage and a coil spring biasing the ball valve toward a valve seat.
Even when the check valve is opened, a flow passage clearance between the ball valve and the valve seat is relatively small. Thus, enough quantity of the working fluid can not pass through the flow passage clearance and a pressure loss of the working fluid is increased due to the check valve. It may cause deterioration in responsiveness of the VVT-controller.
Meanwhile, when a reverse flow is generated, the ball valve receives the reverse flow on its spherical outer surface so that the flow passage is closed. However, a thrust force is hardly generated on the ball valve by the reverse flow. For this reason, a valve-closing-responsiveness of the check valve is deteriorated, so that the responsiveness of the VVT-controller is also deteriorated.